The present invention relates to an automatic tool changing device in a machine tool. More particularly, the invention relates to a type thereof in which a tool assembled to a spindle can be changed with a new tool between a tool magazine and the spindle in accordance with a reciprocating movement of a spindle head.
One example of an automatic tool changing device is disclosed in a Japanese Patent Application Kokai No. 63-267136. According to the conventional device, a cam mechanism is provided for changing a tool with a new tool in synchronism with the ascent and descent motion of a spindle head. This tool changing device provides a machining region where the machining is carried out within the feed range of the spindle head, and an automatic tool change (ATC) region where the actual tool change operation is carried out. In the ATC region, the cam mechanism is operated in accordance with the reciprocal motion of the spindle head to achieve tool changing operation.
In the conventional tool changing device, a machine origin is positively provided between the machining region and the ATC region so as to positively discriminate therebetween in order to prevent the spindle head from being entered into the ATC region during the exact machining. If the spindle head is moved from the machining region to the ATC region and vice versa, the spindle head is temporarily moved to the machine origin (this movement of the spindle head is sometimes referred to as "machine origin restoration"), and thereafter, the spindle head is moved to the other region. So as to perform this temporary restoration, a control device is provided, and a positioning mode is applied when conducting the machine origin restoration.
However, in accordance with the machine origin restoring operation with the positioning mode, the spindle head must be temporarily stopped at the machine origin. Therefore, in case where the tool change is to be conducted with respect to the spindle head positioned on the machining region, the spindle head must be elevated or moved upwardly toward the machine origin, and the moving velocity of the spindle head must be decelerated at a position in the vicinity of the machine origin. The spindle head is then completely stopped at the machine origin, and thereafter, the spindle head is acceleratedly moved upwardly toward the ATC region. Then, tool changing operation is carried out by means of the cam mechanism.
Upon completion of the tool change, the spindle head is moved downwardly toward the machine origin, and is decelerated at a position adjacent thereto, and is then completely stopped at the machine origin. Thereafter, the spindle head is acceleratedly moved downwardly to the previous machining position. For starting the srbsequent machining, the rotation of the spindle is started after the spindle head is temporarily stopped at the machine origin.
Thus, according to the conventional automatic tool changing device, the spindle head must be stopped at the machine origin in an attempt to change the tool with a new tool. Throughout one reciprocal movement of the spindle head between the machining region and the ATC region, twice stops is required in the spindle head. Therefore, entire tool changing period may be prolonged, and accordingly, machining efficiency with respect to a workpiece may be lowered.